Basic Obstetric Ultrasound Periprocedural Care

Updated: May 04, 2021
  • Author: Christine Kansky, MD; Chief Editor: Carl V Smith, MD  more...
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Periprocedural Care

Patient Education & Consent

Elements of informed consent

Most practitioners obtain verbal consent from patients. Ideally, this process should be initiated by the practitioner who requests the study. Risks, benefits, expectations, and limitations of the study should be presented. Some of the limitations relate to the inability of an ultrasound to detect all fetal anomalies, as well as the impossibility to rule out the risk of false-negative ultrasound results.

Additional consent is requested for transvaginal studies.



The physics and principles involving ultrasound are complex, and the curious reader is encouraged to refer to other references for an in-depth discussion of those.

The most important part of the ultrasound machine is the transducer, the tool that makes contact with the patient’s skin. It is equipped with piezoelectric crystals that can generate a sound pulse when excited by an electric current. That sound is released at a specific frequency, travels through human tissue, and interacts with it based on physical properties of the tissue. Sound is absorbed by the tissue, and reflected back to the transducer, where the piezoelectric crystals change that message to electrical impulses that are sent to the processor for interpretation. The processing unit interprets the signals and creates the image we see on the screen.


Patient Preparation


For all diagnostic ultrasound studies and most, if not all, ultrasound-assisted procedures (eg, amniocentesis), anesthesia is not required.


For abdominal studies, the patient is in a supine position for most of the study, with the abdomen uncovered to provide skin contact with the ultrasound transducer. She may keep their clothes on. A coupling gel is used between the transducer and the skin to reduce acoustic impedance from environmental air. This gel may be warmed for patient comfort.

For transvaginal studies, the patient is to remove clothing from the lower part of her body and to lie in a dorsal lithotomy position. Regular stirrups may be used to assist with positioning, or the patient may be asked to assume a frog-leg position. The pelvic area is covered by a blanket for the patient’s comfort. The transvaginal probe is covered with a coupling gel, and a vinyl or latex cover is then placed around the transvaginal ultrasound probe. Another layer of gel is applied around the covered probe to assist in the vaginal insertion and to reduce the acoustic impedance.

Some patients may feel that they are more “in control” of a transvaginal examination if they insert the vaginal probe themselves. Personnel involved in performing transvaginal studies need to be sensitive to patient’s requests. [13]